Sam Kiley

Foreign Affairs Editor

The two men sat widely apart at Charles de Gaulle airport for a brief photograph before getting down to what diplomats like to call a "business-like meeting" - which really means a "frosty encounter".

That the British Prime Minister and the Russian president met at all was a result, though, of overtures from Number 10, officials said.

The British and other members of the G7 think they saw a window. An opportunity for Vladimir Putin to come in from the cold before being frozen out of much of the international economy.

It had been noted that he did not condemn the Ukrainian elections which brought the confectionary king Petro Porochenko to power on May 25.

It had been further noted that the Russian ambassador to Ukraine would be attending the new president’s inauguration in Kiev.

And that Russian troops, at least some of them, had been pulled back from menacing locations close to the border with Ukraine.

These have been interpreted as promising signs that, perhaps, Mr Putin feels he has made his point and is now prepared to reset his relationship with his neighbour to the west.

Such optimism has not been matched with any decrease in violence in eastern Ukraine.

Mr Cameron told Mr Putin the situation in Ukraine is 'not acceptable'

Indeed, as both Barack Obama and David Cameron observed at the G7 in Brussels, Russian weapons and militants to use them have been crossing from Russian territory into Ukraine where they have been locked in bloody battles with government forces.

Not so bloody, yet, it would seem for the G7 to impose the wide sectoral sanctions that they have been threatening Russia with now for close to two months.

Video:Cameron Holds Talks With Putin

This may get wheeled out if there is no improvement over the next month or so, the British and Americans said.

French President Francois Hollande and German Chancellor Angela Merkel are to use Mr Putin's attendance at the D-Day commemorations in France to deliver the same message as Mr Cameron.

"The status quo, the situation today, is not acceptable and it needs to change," Mr Cameron said.

"We need the Russians to properly recognise and work with this new president. We need de-escalation, we need to stop arms and people crossing the border. We need action on these fronts.

"There is an opportunity for a successful, peaceful and stable Ukraine especially now there has been a presidential election."

Video:Cameron Sends Putin 'Clear' Message

Mr Putin may choose to hear the message and to heed it.

But he may choose to interpret it another way.

That the G7 nations and the other alliances that they represent remain woolly. That their fear of the negative effects of sanctions on their own economies is matched by an even more profound reluctance to get involved in any military action in defence of Ukraine.

If he takes that view, then in four weeks' time Ukraine may have descended into a bloody mess resembling some of the worst moments in the Balkan wars of the 1990s.